A Leuconostoc mesenteroides ssp. mesenteroides was isolated from goat's milk on the basis of its ability to inhibit the growth of Listeria monocytogenes. The antimicrobial effect was due to the presence in the culture medium of a compound, named mesentericin Y 105, excreted by the Leuconostoc mesenteroides Y 105. The compound displayed known features of bacteriocins from lactic acid bacteria. It appeared as a proteinaceous molecule exhibiting a narrow inhibitory spectrum limited to genus Listeria, The apparent relative molecular mass, as indicated by activity detection after SDS-PAGE, was 2-5-3-0 kDa. The bacteriocin was purified to homogeneity by a simple three-step procedure: a crude supernatant obtained from an early-stationary-phase culture in a defined medium was subjected to affinity chromatography on a blue agarose column, followed by ultrafiltration through a 5 kDa cut-off membrane, and finally by reverse-phase HPLC on a C4 column. Microsequencing of the pure bacteriocin and of tryptic fragments showed that mesentericin Y 105 is a 36 amino acid polypeptide whose primary structure is close to that of leucocin A-UAL 187, which contains an extra residue at the C-terminus and displays only two differences in the overlapping sequence. However, unlike leucocin A-UAL 187, mesentericin Y 105 displayed a bactericidal mode of action.

A total of 113 strains of mesophilic strains lactic streptococci of the species Streptococcus lactis, S. lactis subsp. diacetilactis , and S. cremoris , chosen from 291 strains that had been previously classified into six groups on the basis of their sensitivity to 132 virulent phages, were subjected to induction with mitomycin C. Among these strains, 43% produced phages capable of forming plaques of lysis on an indicator strain either spontaneously or after induction. There was a close correlation between the lytic spectra of temperate and virulent phages. Among the strains studied, 25% were shown to be indicator strains. These results emphasized the high probability of development of temperate phages in a starter culture containing mesophilic lactic streptococci and therefore their importance as a cause of accidents in cheese making.

Incorporation of [3H]leucine in the bacteria of 18 to 48 h-old colonies of Pseudomonas aeruginosa, Pseudornonas putida, Bacillus thuringiensis, Staphylococcus aureus and Escherichia coli enabled the localization of bacterial multiplication sites by means of autoradiography of sagittal sections. In colonies where fast diameter expansion occurred, all the bacteria from the peripheral corona contributed to peripheral growth; in colonies where the expansion was slower, the growth rate of the bacteria in this region was heterogeneous. Besides this peripheral growth, a central region of bacterial multiplication was always found, but with variable localization and extension. In aerobic species, such as P. aeruginosa and P. putida, the central growth site was limited to the zone of oxygen penetration into the bacterial mass. However, in facultatively anaerobic species, bacterial multiplication depended on nutrient supply. For 48 h-old colonies of S. aureus, a more complex localization of growth seemed to be affected simultaneously by nutrient penetration and accumulation of toxic substances.

Lactobacilli isolated from goats' milk were tested for their inhibitory effects toward Lisleria monocytogenes and Staphylococcus aureus growth. Most of them were antagonistic against these pathogens, as demonstrated by a classical well‐diffusion method and a more sensitive deferred technique, named the ‘sandwich method’. Inhibitory zones, which were largely reduced in the presence of buffered and sugar‐limited medium, were not affected by protease treatment. On the contrary, a few streptococci exhibited inhibitory activity toward L. monocytogenes. Large zones of inhibition were observed, independently of the culture medium and sensitive to protease action, indicating the presence of proteinaceous antimicrobial compounds (bacteriocins). Therefore, the simple sandwich method was sensitive enough to discriminate between antagonistic activities supported by either acid production or bacteriocin action.

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